PB0576 - Correlation between high affinity material for antithrombin and anticoagulant activities of heparin

Background: Clinical heparin comes from two main sources – porcine or bovine mucosa. These two sources of heparin have different specific activities when measured by the two antithrombin dependent anti-Xa and anti-IIa assays. Activity mediated by antithrombin depends on the presence of the pentasaccharide within heparin, the relative quantity of which can be measured by a fluorescence titration assay. This proportion of high affinity material (HAM) can give an indication of the potential anticoagulant activity of heparin.

Aims: To study the relationship between activity and HAM for bovine and porcine heparins

Methods: The activity and molecular weight (Mw) of the heparin samples were measured using the United States Pharmacopeia methods. A fluorescence titration assay was used to determine the HAM in each heparin sample. Spearman rank correlation was carried out between the results to determine any differences.

Results: The correlation between HAM and the activity or Mw of heparin samples is shown in table 1. No correlation was observed between HAM and anti-Xa activity, whilst only bovine heparin shown a correlation between HAM and anti-IIa. For both porcine and bovine heparin the Mw and ratio of anti-Xa/anti-IIa both correlated with HAM.

Conclusion(s): Irrespective of heparin source, an increase in Mw correlated with proportion of HAM indicating that ‘more’ higher Mw heparin translates to the presence of more pentasaccharide (HAM). However, whilst higher potency for bovine heparin correlated with HAM, this was not observed with porcine heparin. For porcine heparin, the lack of correlation could be due to the higher amount of HAM leading to saturation of the anti-IIa template mechanism.